Numerical Analysis of Multispecies Solute Transport through Heterogeneous Porous Media

A numerical approach to the decomposition method for the study of multispecies solute transport through heterogeneous porous media has been proposed. Governing equations of multispecies solute transport have been solved numerically using the implicit finite difference technique. The effect of time-dependent dispersion has been analyzed using exponential time-dependent dispersivity function and the same has been validated with the analytical solution. The study illustrates the solute movement involving sequential first-order decay reactions and the analysis has been carried out in three species nitrification chain and migration of radionuclides as four species. The numerical model is used to simulate the breakthrough curves and the analysis has been done using different decay rate constants. Also, this study has been carried out on the behavior of solute concentration using an increasing macrodispersivity function which accounts for the spatial heterogeneity of porous media. Further, spatial moment analysis has been performed on the concentration of all species and a comparison has been drawn using constant and exponential time-dependent dispersivity function using various breakthrough curves. This analysis revealed that the mean travel distance and variance are sensitive with the change in the dispersivity function and concludes that the solute and its transformed species may not have the same transport pattern.